The SSTab control works by moving all the controls that are on other tabs off the screen by 75000 twips or so. When you changes tabs, the controls that were shown are moved off and the controls to be shown are then moved into view.

If you have any code that would effect their movement,if the controls themselves have a slow redraw, or you simply have a very large number of controls on each tab then you may witness a small delay. This should almost never happen on any current processor but if you are using older technology it might be more noticable.